Introduction: Singing is a physical activity with less reliance on skeletal muscle and more dependence on the diaphragm and cardiorespiratory systems. Unlike traditional exercise, the impact of singing on vascular health has not been studied. We hypothesized that older patients with known coronary artery disease (CAD) would have a favorable improvement in vascular endothelial function after 30 minutes of singing. Methods: Adult subjects with known CAD were recruited from cardiology clinics to participate in two singing sessions 30 minutes each and one control (rest period) session 2 to 7 days apart, according to a randomized, controlled, single-blind, crossover design. The two singing intervention sessions were (1) a pre-recorded video with a voice professor directing a ‘patient’ singing and (2) live singing coaching with a music therapist. Microvascular function was measured with peripheral arterial tonometry (PAT) before and after singing and expressed as Framingham reactive hyperemia index (fRHI). Macrovascular function was measured with brachial artery flow-mediated dilation. Cross-over treatment estimates of video, coaching, and control sessions were obtained with unbalanced ANOVA including the following variables: subject, the order of their visit, treatment, and its carry-over. Results: Sixty-five subjects (40% women, mean age 68±7) with CAD completed the study. Comorbidities included type 2 diabetes (29%), hypertension (75%), hyperlipidemia (85%), heart failure (19%), and self-reported physical or orthopedic limitations (54%). Compared to the control visit, there was a 26.5% (SE11.1%, p=0.0192) increase in fRHI in the video visit and a 17.3% (SE 10.7%, p=0.1081) increase in fRHI in the coaching visit. There was a small carryover effect with the video visit. There was no change in macrovascular endothelial function across the three different visits. Conclusions: Thirty minutes of singing improved microvascular endothelial function but not macrovascular endothelial function, in older patients with known CAD. This represents a potential biologic mechanism by which singing can benefit the cardiovascular system. Future studies should explore the sustained vascular adaptation to singing over weeks to months of singing.